Objective Morbid obesity is associated with a higher independent risk of chronic kidney disease (CKD). Estimated glomerular filtration rate (eGFR) has been evaluated in a limited number of study participants with severe obesity. Methods A total of 706 measured GFR (mGFR) results from 598 participants with obesity (BMI ≥ 35 kg/m2) were retrospectively collected. The performance of the Modification of Diet in Renal Disease (MDRD) equation, Chronic Kidney Disease‐Epidemiology (CKD‐EPI) equation, and deindexed eGFR were compared with mGFR from the gold standard technique (inuline or iohexol), adjusted (mGFRr) or nonadjusted (mGFR) to body surface area. Absolute bias, precision, and accuracy were calculated. Results Mean mGFRr (58 ± 31 mL/min/1.73 m2) was significantly different from CKD‐EPI and MDRD (P < 0.001). Mean mGFR (nonindexed) (70 ± 40 mL/min) was significantly higher than mGFRr (P < 0.001). eGFR showed important biases and low accuracies for CKD‐EPI and MDRD (10.7 ± 10.7 and 12.2 ± 13.7 mL/min/1.73 m2; 78% vs. 75% respectively). Deindexation worsened bias and accuracy 30% (percentage of GFR estimates within 30% of mGFRr or mGFR) between eGFR and mGFR. Conclusions eGFR overestimates mGFR and is associated with important biases and inaccuracies in patients with severe obesity, and deindexing eGFR worsens the overestimation. These findings may have important implications in examining kidney function in patients with obesity.

<b><i>Introduction:</i></b> Living donor kidney transplant (LDKT) is one of the best therapeutic options for end-stage kidney disease (ESKD). Guidelines identify different estimated glomerular filtration rate (eGFR) thresholds to determine the eligibility of donors. The aim of our study was to evaluate whether pretransplant donor eGFR was associated with kidney function in the recipient. <b><i>Methods:</i></b> We retrospectively studied LDKT recipients who received a kidney graft between September 1, 2005, and June 30, 2016 in the same transplant center in France and that had eGFR data available at 3, 12, 24, and 36 months posttransplant. <b><i>Results:</i></b> We studied 90 donor-recipient pairs. The average age at time of transplant was 51.47 ± 10.95 for donors and 43.04 ± 13.52 years for recipients. Donors’ average eGFR was 91.99 ± 15.37 mL/min/1.73 m². Donor’s age and eGFR were significantly correlated (<i>p</i> &#x3c; 0.0001, <i>r</i>² 0.023). Donor’s age and eGFR significantly correlated with recipient’s eGFR at 3, 12, and 24 months posttransplant (age: <i>p</i> &#x3c; 0.001 at all intervals; eGFR <i>p</i> = 0.001, 0.003, and 0.016, respectively); at 36 months, only donor’s age significantly correlated with recipient’s eGFR. BMI, gender match, and year of kidney transplant did not correlate with graft function. In the multivariable analyses, donor’s eGFR and donor’s age were found to be associated with graft function; correlation with eGFR was lost at 36 months; and donor’s age retained a strong correlation with graft function at all intervals (<i>p</i> &#x3c; 0.001). <b><i>Conclusions:</i></b> Donor’s eGFR and age are strong predictors of recipient’s kidney function at 3 years. We suggest that donor’s eGFR should be clinically balanced with other determinants of kidney function and in particular with age.